xov., 1961
SOTES
2105
average pore size. The relationship could be determined by calibration against a primary poresize measurement. The range of 10 to 1000 A. in pore diameter would be involved. If the method were to be used, adsorbent granules should be of the same over-all dimensions to avoid differences in the rate of flow between granules. At least one granule dimension should be greater than 1 millimeter so that the inter-granular flow does not become ratelimiting.
noticed. The epitaxially grown nickel films mostly developed parallel orientations. They were occasionally mixed with a small amount of crystals which were aximuthally rotated by 4 j 0 , ie., they thus had (110) axis parallel to (110) axis of NaC1. { 111] twinned structures of the oxide were observed also. In some cases the patterns due to unknown oxide were predominant. Using 220 rings of either X i 0 or Xi, the dhkl values were evaluated and rings indexed. Table I shows thme values which agree well with a hexagonal structure having a. = 4.61 A., co = 5.61 A. and colao= 1.22. AN OXIDE OF TERVALENT NICKJ3L It is, however, interesting to note that cobaltic oxide (Cos03) has a similar hexagonal structure BY P. S.AGGARWAL AND A. GOSWAMI (UO = 4.64 A., co = 5.75 A., eo/@ = 1.24) with its d National Chemical Laboratorv, Poona-8, Indza values and intensities of rings4 very close to those of Recaved Aprzl 1 1 , 1961 the oxide of nickel mentioned above (Table I). From While iron and cobalt exist in di- and tervalent the consideration of similarities in the properties of states in the oxides of compositions MO, M20; cobalt and nickel compounds and their isomorand M304, the existence of anhydrous Ni203 has phous nature and also of the fact that similar been doubted by many workers. Attempts to pre- chemical compounds have similar structures, it pare this by heating the hydroxide, basic carbonate may be concluded that the observed hexagonal or nit,rate of nickel in air or oxygen resulted in the structure is very likely due to the formation of formation of NiO only.' Cairns and Ott2 prepared the oxide of tervalent nickel (Xi203),as in the from solutions a compound of the composition case of cobaltic oxide (Co207). It may, however, yi~O3.2H20, which decomposed to NiTOs H20 be pointed out here that, in the absence of accurate and finally to KiO, as revealed by X-ray studies. intensity data of Co108 the comparison cannot he No line characteristic of S203was a t all detected. carried out too far. Rooksbya showed, by X-rays, that different oxides ( 4 ) A S.T.N. Card No. 2-0770. of nickel, Hack or otherwise, obtained from various sources consisted only of N O . During electron diffraction studies of evaporated films of nickel, on PRIMARY STEPS I N THE PHOTOLYSIS OF hot rocksalt substrates in uucuo, me observed many METHYL CARBONATE' rings in diffraction patterns, which could not, be BY M. H. J. WIJNEN explained by the presence of Ni and 5 0 alone, but Radzatzon Research Laboratotzes, Mellon Instztutr. Pittsburgh. P a . required the esistence of an oxide having a hesaRecezved M a v 1, 1961 gonal structure. Nickel was evaporated from a nickel filament Investigations of the photolysis of methyl ace(spec. pure, supplied by MIS.Johnson and Matthey tate2.3have shown that the main primary process & Co., London) a t a pressure of about 10-' to produces methoxy radicals according to mm. (obtained by a rotary oil pump) on the cleavCHZCOOCHT + h v --+ CHSCO + CHBO age face of rocksalt crystals kept a t about 400'. After removal of the films from the substrate in the A similar step in the photolysis of methyl carbonate usual way. these were examined in the E D . cam- would lead to CH3OCO and CH30 radicals and possibly to 2CH30 and CO if the CH30C0 radiera by transmission methods. cals would decompose into carbon monoxide and TABLE I" methoxy radicals. This investigation has been a0 = 4 . 6 1 m = 4.64 undertaken to investigate the feasibility of using ci, = 5 . 6 1 co = 5.75 Ni20z co/m = 1 . 2 2 CorOa' co/m = 1 . 2 4 the photolysis of methyl carbonate as a source for Intensity d Intensity hkl d (X-rays) methoxy radicals.
-
3.23 2.80 2.30 2.02 1.77 1.62
vf
..
..
S
m3 S
p 3
101 002 110 200 112 202 21 0 004
3.21 2.87 2.33
.. 1.78 1.63 1.57 1.39
1.40 f 1.11 f ... ... a v, very; f , faint; s, strong; and m, medium.
90 100
100 I
.
.
100 90 -50 90
...
Pat terns thus obtained, consisting of rings and spots, mostly were due to nickel, though sometimes extra rings of X i 0 and the unknown oxide were (1) R. W. Cairns and E. O t t . J . A m . Chem. Soc., 65, 527 (1933). (2) R. W. Cairna and E. Ott, ibid., 66, 534 (1933). (3) H. P. Rooksby, Nature, 162, 304 (1943).
Experimental Since it has been observed4 that methyl carbonate decomposes thermally on quartz, the photolysis was studied at 6 and a t SO" only. The usual photochemical technique hab been applied. A Hanovia Type 73A10 (S-500)medium pressure arc was used to obtain the data a t SO". Constant temperature a t 80" was maintained by an aluminum block furnace. Temperature control a t 6' was obtained by placing the cell in a mater-bath and transmitting the light through a 5 mm. layer of water into the cell. A Hanovia medium pressure arc (Type 16A13) was used as the light source for the experiments at 6". Analyeis of the reaction products (1) ThiR investigation was supported, in part, by the U. S. iltoniic Energy Commission. (2) (a) W. L. Roth and G. K. Rollefson, J . A m Chem. Soc., 64, 490 (1942); (b) P. .4usloos. Can. J . C h e m , 36, 383 (1958). (3) (a) M. H. J. Wijnen, J . Chem. Phys., 27, 710 (1957); (b) 28, 271 (1958): (c) 28, 939 (1958). 4 ' (4) M. H. J. Wijnen, abad., 34, 1465'(1961).
was carried out by gas chromatography. The following reaction products were observed: CO, CO?, QH,, C2HB, CHaOH, CHIOCH, and CH20. No quantitative analysis was carried out, for formaldehyde. The amounts of methyl ether produced were too small to be measured accurately. Table I gives the observed product distribution under various conditions of light intensities and initial pressures. The conversion was on the order of 0.5y0of t,he starting materid.
The recombination of methyl radicals, produced by step l a , is suggested as the sole mode of ethane formation. Step l a also produces methoxy radicals which may form methanol via disproportionation and/or hydrogen abstraction. The amount of methanol produced by step IC,if occurring, could not exceed twice the amount of CO produced. Our results a t 80" indicate that RCH~OH >> 2Rco Discussion thus confirming step l a also through the production Within experimental error CO and COZ are of methanol. directly proportional to incident light intensity and The large yield of GOz indicates clearly that prito initial pressure. Accepting, therefore, that they mary steps la and l b constitute a major part ofthe are produced in the primary process, the steps to be total primary process. Steps ICand/or Id are sugconsidered are gested to explain the formation of carbon monoxide. (CH3C))XO + hv ---+ CH3 CO? CHIC) (la) Since methoxy radicals produced by step IC may +CH, + COz CHzO (lh) form methanol and formaldehyde it is difficult to +2CH20 + CO (IC) choose between these two steps. K e are inclined +CHIOH + CO + CHzO ( I d ) to give a slight preference to step Id based on the It is obvious t'hat, as an intermediate t'he CH3OCO follotving observation. We may calculate the radical may have been formed. Attempts to importance of the CO and CH, producing primary identify methyl oxalate and methyl acetate as steps if we accept Reo RCo2as a measure of the reaction products failed. This indicat'es that under total primary process. Such calculations indicate our experimental conditions the CHBOCO radical that the fractions of the primary process leading to must decompose readily if formed. Surprising is CO and CHI are roughly 0.14 and 0.4 a t 6" and 0.08 the relatively large amount of methane formed. and 0.23, respectively, at 80". This is not necesIn addition to primary step lb, methane could sarily a temperature effect since different light conceivably be produced by the reactions sources and thus possibly different wave lengths were used. The contribution of the CO and CHI CH, + CH30 +CH, CHzO (2) producing steps to the total primary process thus (?Ha + (CH30))CO +CHI + R (3) varies considerably with the experimental conditions TABLE I of our investigation. Nevertheless, the ratio PHOTOLYSIS OF METHYL CARBONATE RCO/RCH remains ~ approximately constant. This (CHaO)?- IntenCO. sity indicates that CO and CH4 may originate from the relamolec. same electronic excitation level. This would be tive Rco R C O ~ R C H ~ R c ~ H R~ C H ~ O H cc. X 10 vc Product rates in molec./sec. cc. X 10-10 the case if CO is produced by molecular rearrangeTemp., 6' ment step I d which is similar to the production of 100 29.0 102.1 70.1 28.0 4.84 85.0 methane by step lb. This consideration does not 100 13.2 li0.7 1.80 30.0 5.4 32.9 exclude the possibility that step ICalso may occur 9 2.0 11.4 7.9 4.80 1.5 0.8 9 1.9 12.1 6.4 1.2 to some extent. Our data do not suggest the occur4.12 4.2 5.28 26 5.9 41.3 21.G 4.2 21.0 rence of primary steps other than steps l a to Id. 00 8.3 49.5 20.3 4.5 1.81 27 1 It is clear from primary steps l a and l b that 41.8 4.43 30 0.1 15.1 0.7 20.5 (RcH~ 4- ~ R C ~ H ~ ) /should R C O ~be equal to unity. Temp., SO" The actual observed value indicates ( R c H ~ 100 208.6 159 51.4 12.60 45.9 122.8 2 R c 2 ~ J / R c o'va 0.7. This deficiency in methyl 93.4 100 9.5 24.0 21.6 6.58 47.0 radicals may be explained by the addition of 100 5.9 61.1 3.65 18.7 8.2 28.8 100 157.5 11.9 34.3 11.78 33.1 fi1.2 methyl radicals to the CH20COOCH3radical which 11.95 2.5 2.R 31.5 7.0 6.5 17.7 is produced by the reaction
+
+ +
+
+
-1:
+
11.81 11.90
9 50
1.4 6.0
17,s 72.4
3.6 15.5
Previous results3bindicate t'hat kJk4 k q is the rate const'ant of reaction 4). CHI
3.2 13.1
'v
+ CH3O +CH,OCH,
fj.4
50 7
1.4 (where (4)
Since only trace amounts of methyl ether have been detected, reaction 2 may be excluded as contributing in :my appreciable extent to t'he amount of methane produced. Reaction 3 undoubtedly requires an activation energy of not less than 8 kcal. in analogy to other activation energies for the abstraction of a primary hydrogen by methyl radicals. This re:iction thus is not likely to occur to any large extent at the relatively low temperatures of our investigation. It therefore seems reasonable to suggest primary step l b as the main source of methane production. It may be mentioned that molecular rearrangements have been observed also in the photolysis of other esters.2b
CH3O
+ (C'H30)XO +CHjOH + CHzOCOOCH3
That methoxy radicals are able to abstract primary hydrogens at the relatively low temperatures of our investigation has been shown previ~usly.~ Since me have not analyzed for formaldehyde, it is not possible to carry out material balance calculations for the methoxy radical. Acknowledgment.-The author wishes to express his sincere thanks to Mr. J. A. Guercione for his aid in this investigation. VA4POR PRESSURES OF PLATINUBI METALS. 11. RHODIUM BY LLOYDH. DREGER AND
JOHN
L. MARGRAVE
Department of Chemistrv, Uniuereity o f W h c o n s i n , Madison, Wisconsin Received M a y 87, 1961
N e w vapor pressure data are reported here for
